Indium tin oxide (ITO) is the most widespread transparent conductor in optoelectronic applications. However, the mechanical rigidity of ITO limits its use for flexible devices such as wearable electronics, displays and photovoltaic devices.
Graphene is transparent, conducting and bendable but is also a very strong material. However, the lowest values of graphene's sheet resistance are far above the values of commercially available ITO, i.e. 10 Ω/□ at an optimal transmittance (Tr) of 85%. Many efforts have been made at decreasing the sheet resistance of graphene-based materials whilst maintaining a high transmittance in order to harness the potential of graphene-based materials in optoelectronic applications. Up until now, the best values of sheet resistance and transmittance of graphene-based materials are still far from the performances of ITO with typical values of sheet resistance being 30 Ω/□ at a transmittance of 90% for graphene multilayers and 125 Ω/□ at a transmittance of 97.7% for chemically doped graphene.
In order to replace ITO in optoelectronic applications, it is generally agreed that the replacement material must at least have the properties of commercially available ITO.
Whilst the intercalation of bulk graphite with a large variety of molecules results in a charge transfer and an enhancement of the conductivity, it is not clear whether few-layer graphene materials (FLGs) can also be intercalated by a similar method as well as it is not clear if these intercalation compounds would affect the optical transparency of FLGs. Furthermore, it has been found that most graphite intercalation compounds are unstable in air, with donor compounds being easily oxidised and acceptors being easily desorbed.
Some air stable graphene intercalated compounds can be used but these have to be synthesised in the presence of chlorine gas which is highly toxic and therefore it is undesirable to use those compounds. Further, the intercalation temperature is typically high, more than 500° C., and therefore incompatible with flexible plastic substrates.